Add fio_cpuset_exit() empty handler for platforms that don't support affinity

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/os/os.h b/os/os.h
index 823b039..5a3bc55 100644
--- a/os/os.h
+++ b/os/os.h
@@ -42,6 +42,7 @@
 #define fio_setaffinity(td)		(0)
 #define fio_getaffinity(pid, mask)	do { } while (0)
 #define fio_cpu_clear(mask, cpu)	do { } while (0)
+#define fio_cpuset_exit(mask)		(-1)
 #endif
 
 #ifndef FIO_HAVE_IOPRIO